The present invention relates to a method for producing an improved shea fat suitable for a hard butter.
It is well known that a shea fat is used as cacao butter substitute. For this purpose, the shea fat has been used as it is in a few cases, but in most cases, it has been fractionated with an aliphatic ketone such as acetone or methyl ethyl ketone into two portions, one being a hardly-soluble portion consisting of some impurities such as karitene and another one being a readily-soluble portion mainly consisting of certain unsaturated glycerides, in particular, SOS (stearyl-oleyl-stearyl-triglyceride). The latter fraction is used as a cacao butter substitute as it is, or in the form of a mixture with an intermediate fraction of palm oil (hereinafter, referred to as "palm mid-fraction") with or without further fractionation (cf. British Patent Specification No. 925,805). However, such hard butters generally are inferior in the tempering properties upon chocolate-making when they are admixed with the conventional ingredients for chocolate such as cacao butter, milk, sugar, etc. This defect is particularly remarkable when a considerably large amount of the above palm mid-fraction is used, or when fatty ingredients different from those of the cacao butter, such as a milk fat as in a milk chocolate, are additionally used. As is generally known in this field, in the standardized chocolate industries at the present time, there has customarily been used an automatic tempering apparatus in which the raw materials are automatically subjected to a predetermined temperature/timetreatment and then poured into a shaping mold. In this automatic process, it is required to control the temperature during the treatment, wherein the raw materials are cooled to a crystallizing temperature from the higher melting temperature and are again warmed to a slightly higher pouring temperature. Moreover, it is also required that the raw materials themselves are to have a workable viscosity as low as possible, even at the tempering temperature which is the lowest temperature during the above heat treatment and further to have a sufficient temperature difference between said tempering temperature and a critical temperature which means the highest temperature at which the viscosity of the materials increases so high as to make the practicing of the process impossible. If this temperature difference is too small, it is necessary to control the working temperature very precisely over its automatically controllable range, and further, even if such a control has been made, the separation of the molded chocolates from the shaping mold often becomes difficult. Another problem in the conventional shea fat is that shea nuts from which the shea fat is extracted easily deteriorate during the storage thereof. As is well known, the quality of the shea fat becomes markedly worse when the shea nuts are kept for a long period of time after the crop is harvested because of the auto-hydrolysis of neutral oils and fats contained in the nuts or because of the complicated chemical changes of the isoprene polymer components thereof, and therefore, the hard butters prepared from such deteriorated shea nuts are mostly undesirable for confectionaries. Since this deterioration initiates so soon after the nuts have been cropped, it occurs more or less before pressing. In particular, the shea fat pressed out from the old crop will be only slightly refined, which causes a great problem in the production thereof.
Moreover, it is a significant problem in this field that the conventional hard butters composed of a mid-fraction of shea fat fractionated with a ketonic solvent and the palm mid-fraction have inferior tempering properties. This reason has not been made clear but it is assumed that the inferior tempering properties thereof may be caused by the aforementioned complicated deterioration of the nuts, by which an unknown tempering hindrance factor (hereinafter referred to as "THF") is accumulated in the nuts as the deterioration proceeds. We have found that this undesirable THF can be eliminated from the crude fats according to the present invention.
It has hitherto been considered that the impurities in shea fat are karitene which is a polyisoprene compound with an unknown chemical structure, terpenes and sterols. Among them, karitene can mostly be removed by a fractional crystallization since it is hardly soluble in the aforesaid ketonic solvents, while the latter two impurities can also be separated from the intermediate fraction mainly consisting of stearyl-oleyl-stearyl-triglyceride since they are very easily soluble in the ketonic solvents. However, we have found that the conventional shea fat contains a further impurity: THF which badly influences the tempering in the intermediate fraction of the shea fat fractionated in a usual manner, and the removal of this factor is economically impossible so long as the usual refining method is utilized. The present invention provides an economical method for removing THF in the shea fat.
The main object of the present invention is to provide a method for producing an improved shea fat suitable for a hard butter superior in its tempering properties by an economical process. Another object of the present invention is to make possible the use of aliphatic hydrocarbon solvents such as n-hexane, which are permitted as food additives by the Food and Drug Administration, but have heretofore been regarded as improper for the fractionation of shea fat. A further object of the present invention is to improve the tempering properties of the shea fat derived from deteriorated shea nuts. A still further object of the present invention is to make possible the omission or simplification of the usual deacidification step and further to make easy the refining of shea fat. These and other objects and advantages of the present invention will be appearent from the following description.
As a result of extensive studies on the refining manners of shea fat, the inventors have now found that the THF will be included in the fraction which is easily soluble in lower aliphatic alcohols (hereinafter referred to as the "alcohols"). Based on this finding, it has been found that the improved shea fat can be produced by removing the easily-alcohol-soluble portion of the shea fat by treating it with alcohols.
Heretofore, it has been known to fractionate crude shea fat for the production of the fat for soap-making, by treating with boiling ethanol, removing the insoluble materials by decantation, and cooling the resulting solution to separate it into only slightly soluble or insoluble portions and readily-soluble portions (Bull. Mens. Inform. IPERG 7, 395-6, 1958). However, according to our investigations (refer to the aftergoing Comparative Example 1), the yield of the crystalline portion obtained by this fractionation was only 51% by weight, and it showed a high iodine value of 47 and its coagulation properties (cooling curve) were also not improved. If such fractionated fat were used for chocolate-making, there would be required a very precise temperature control of the tempering process and the chocolate thus produced would be unsatisfactory in its snapping property which is the life-line of chocolates.
The method of the present invention comprises a combination of the following steps. At first, the raw shea fat and alcohols are mixed together. The alcohols is used in an amount enough to completely dissolve the neutral oils and fats and further almost sufficient to separate out the alcohols-insoluble ingredients in the shea fat. This amount varies depending on the kinds of alcohols used, but for example, in case of an ethanol having a concentration of 85% by weight or higher, it is used in a range of 1 to 20 parts by weight to 1 part by weight of the shea fat. The use of larger amounts of ethanol is not economical. So-called "denatured ethanol" which is contaminated with a small amount of hexane may also be used instead of pure ethanol. The alcohol mixture is then heated and allowed to stand at the same temperature in order to remove the precipitated alcohol-insoluble materials. Next, the mother liquor is cooled to separate into the oil-poor upper layer (alchohlic phase) and the lower layer (oily phase), and then the latter is collected by flowing down. Besides, the former (the alcholic layer) can be repeatedly used for the following refining process without distillation, but limitless recycling of this layer will cause a decrease in the effect of the refining because of the accumulated free fatty acids and THF therein. Therefore, it is preferable to remove a part of the alcoholic layer from the system continuously or from time to time in a predetermined interval. The amount of the alcoholic layer to be removed should be determined according to the cooling curves of the final products, however, usually it is 5 to 20% by weight of the alcohols used in each refining procedure. Of course, if an undeacidified shea fat is used as the raw material, a larger amount of it should be removed.
It is preferable to lower the cooling temperature as low as possible for separating the alcoholic layer and the oily layer, since the lower the temperature, the less the solubility of oils and fats in the alcohols. But, generally speaking, a range of 20.degree. to 60.degree. C. is preferable. As the alcohols, propanol, isopropanol and so on may be used as well as ethanol.
The lower oil-rich layer obtained above is then subjected to a conventional solvent fractionation process. That is, the lower layer is dissolved in an organic solvent (e.g. n-hexane, acetone or methyl ethyl ketone) and the resulting crystalline portion is separated by filtration to give the desired improved shea fat.